提示：1）树能吸收有害气体，能给我们提供氧气。树能清洁空气，是对抗空气污染的好战士；

2）我们生活中有很多东西都来自于树木，比如书桌、椅子、门和床等等；

3）树给我们提供水果；

4）树还可以美化我们的城市。

Trees are very helpful to us

    Do you know who invented paper? A Chinese man1Cai Lun invented paper almost 2,000 years ago. He made paper2wood.

    Now we still use wood3paper. We use a lot of paper every day. If we keep on4so much paper, there will not be any trees left on the earth. If5no trees, there will be no paper. Every day, people6about 2,800 tons of paper. We use 17 trees to make one ton of paper. This means we are cutting nearly 48,000 trees every day.

    Since it7more than 10 years for a tree to grow, we must start using8paper now. So how can we save paper? We can use both sides of9of paper, especially when we are making notes. We can choose drinks in bottles instead of those in paper packets. We can also use cotton handkerchiefs (手帕). When we go shopping, we can use fewer paper bags. If the shop assistant gives us a paper bag, we can save it and reuse it later.

    Everyone can help to save paper. If we all think carefully, we can help10trees. But we should do it now, before it is too late.